Various electronic "digitizer pens" are used in conjunction with electronic digitizers, digitizer tablets, or the like. Such digitizer pens include replaceable ink cartridges used both for writing and mechanical activation of an internal "pen switch" when the tip of the replaceable ink cartridge is pressed against a digitizing surface of the digitizer pad or tablet to control the electronic operation of the digitizer pen in the digitizing process. (Although inking capability is not needed for digitizing of information that already is imprinted on a sheet of paper, use of an ink cartridge in a digitizer pen allows information to be digitized as it is being written on a sheet of paper placed on the digitizing surface.) Many of the prior digitizer pens are cordless and therefore battery powered. This necessitates efficient use of power to prolong battery life. In order to obtain an optimum transfer of the "pen signal" from a "pen coil" into the receiving grid conductors of a digitizer tablet, the highest possible signal strength must be achieved with the minimum dissipation of power. This necessitates use of an annular, cylindrical ferrite core around which the pen coil is wound and through which the writing tip of the ink cartridge extends.
A problem with prior electronic pens is that it is difficult to replace spent ink cartridges because a fixed ferrite core of the pen coil is positioned coaxially about the writing tip end of the ink cartridge so that only a very small portion of the writing end of the cartridge is ever exposed beyond the end of the ferrite core. This makes it very difficult for the user to grasp a spent ink cartridge sufficiently securely to remove it so it can be replaced with a new one.
While "standard" and non-standard ink cartridges have been used in various prior digitizer pens, for example as disclosed in U.S. Pat. Nos. 4,532,376, 4,638,119 and 4,227,044, which utilize pen coils, none of these references disclose a more modern digitizer pen structure in which the writing end of an ink cartridge extends through a fixed ferrite core around which a pen coil is wound, and none of these prior digitizer pens present the above-described difficulty of removing a spent ink cartridge from the pen barrel. One prior approach to solving this problem has been to provide special ink cartridges for use in digitizer pens, wherein the tip can be somewhat more easily grasped is the case for standard ink cartridges. Another approach, for example in a digitizer pen made by WACOM of Japan, is to provide an ink cartridge removal tool which is especially adapted to remove non-standard ink cartridges of its own design.
However, it would be much less expensive and more convenient to provide a digitizer pen in which standard, inexpensive, widely available ink cartridges can be used and in which they can be easily removed and replaced without using a specialized tool, or even any tool at all.